Hepatitis B virus (HBV) is the prototype of the hepadnavirus family, which includes hepatotropic viruses that infect at least six separate species. Infection with HBV causes polymorphic liver diseases including acute or fulminant hepatitis, chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Over 300 million people throughout the world are chronically infected with HBV and are at high risk of developing hepatocellular carcinoma, one of the world's most prevalent forms of cancer. Within the last year we pursued two avenues of investigation. First, we continued our characterization of a putative neutralization escape mutant of HBV that emerged in individuals who were vaccinated against hepatitis B. Two licensed vaccines were investigated for their ability to protect chimpanzees against challenge with the S gene mutant. Both recombinant vaccines provided protection against challenge with the mutant suggesting that properly vaccinated individuals are not at risk of infection by the S gene mutant virus. Second, a bi-directional promoter complex was iden- tified within the X gene of HBV further emphasizing the complex genetic organization of this virus.